| Value of sum for n=126 has been checked to be probably prime with the isprime functions of PARI and Maple V. Also checked with ECM - see link.
Note that n+1 must be prime and hence a(k)=A088856(k)-1. Another way to compute the number is (n^(n+1)-1)/(n-1). - T. D. Noe (noe(AT)sspectra.com), Dec 15 2004
Value of sum for n=126 has been certified prime with Primo. - Ryan Propper (rpropper(AT)stanford.edu), Jul 11 2005
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